This study relates to the modification of 2-benzylamino-4 methyl-6-trifluoromethyl-1,3,5-triazine. New 1,3,5-triazine compounds with an electron-withdrawing carboxyl group, e.g. ester group, substituted for the trifluoromethyl group, were synthesized and assayed for activity to inhibit photosynthetic electron transport (PET) in thylakoids of spinach as well as both atrazineresistant and wild-type Chenopodium album. Among the compounds with an alkylamino group, 2-ethoxycarbonyl-4-isopropylamino-6-methyl-1,3,5-triazine was the most potent PET-inhibitor, exhibiting a pI50 of 6.11. The inhibitory activity was generally more potent with 2-alkoxycarbonyl-4-(branched alkyl)amino-6 methyl-1,3,5-triazines than amino-analogues with straight chain alkyl groups or unsaturated alkyl groups.